1. Field of the Invention
The present invention relates to a method and apparatus for controlling the thrust of an aircraft engine using a single lever power controller.
2. Related Background
A plurality of levers are required to control aircraft engines in general aviation, commercial aviation, and unmanned aircraft. For example, a throttle lever is required to control the throttle blade, a fuel mixture lever is required to control the fuel mixture, a propeller pitch lever may be required to control the RPM of the propeller or turbine fan, a waste gate lever is typically required to control the exhaust waste gate in engines which are turbo-charged, a propeller governor lever is often required to control the propeller governor, etc. The pilot is required to control all of these levers simultaneously to achieve the most efficient engine performance for the given flight conditions. This is often a hit-and-miss procedure based on the pilot""s experience, and thus the engine generally is not optimized to operate in a fuel-efficient manner to produce the optimum thrust. Also, continually monitoring these many control levers increases the pilot""s workload leading to pilot fatigue and reduced attention to other necessary pilot tasks. In an emergency situation, the pilot may not be able to achieve optimum engine control, leading to engine failure or loss of controlled flight. These problems are exacerbated in unmanned air vehicles (UAV=s) since the pilot is remote from the aircraft and lacks sensory input regarding flight conditions.
In the field of engine control, many proposals exist for controlling the flow of fuel to the engine in accordance with detected engine operating parameters such as engine temperature, engine pressure ratio, shaft speed, etc. to maximize fuel efficiency, but such proposals fail to take into account the ambient operating conditions. Proposals of this type are described in U.S. Pat. Nos. 4,248,042; 4,551,972; 4,686,825; 5,029,778; 5,039,037; 5,277,024; and 5,613,652. However, even if such systems were adapted to aviation, the pilot would still be required to operate and continually adjust a plurality of control levers to optimize engine thrust for given flight conditions.
By 1985, it was recognized that aircraft engine efficiency is highest when the engine is run with the throttle butterfly valve fully open and the desired performance is obtained by varying propeller speed. See, for example, SAE Technical Paper Series 850895, Athe Porsche Aircraft Engine P F M 3200xe2x80x3, Helmuth Bott and Heinz Dorsch, 1985. This article proposed a single-lever control system for an aircraft engine that operates both the throttle and the propeller governor with a single lever. However, the proposed system is a mechanical linkage system which accordingly cannot optimize engine performance based on various ambient flight conditions. That is, the Porsche system may work well at a single altitude, speed, and temperature, but will seriously degrade at other flight conditions.
Thus, what is needed is a single lever power controller apparatus and a method for controlling an aircraft engine to achieve the maximum thrust efficiency throughout the flight performance envelope of the aircraft.
The present invention is intended to overcome the drawbacks of known aircraft engine control systems by providing a processor-controlled system which inputs a single thrust or power command, receives detected ambient flight conditions, and automatically controls the engine speed, (e.g., propeller RPM) and engine load (e.g., manifold air pressure (MAP)) for the detected flight conditions and relative to the requested thrust or power command.
According to a first aspect of the present invention, a single lever power control apparatus for controlling an aircraft engine includes a single, manually-operable lever for generating a pilot thrust command. A processor receives the generated pilot thrust command, receives a plurality of detected ambient air conditions, and determines an engine speed activation command and an engine load activation command based on the maximum thrust efficiency for the detected ambient flight conditions and thrust command. In one embodiment, the thrust efficiency optimization is performed off-line where the processor accesses a look-up table which stores highest thrust efficiency values for the detected flight conditions and thrust command. In another embodiment, the optimization is performed on-line where the processor determines the highest thrust efficiency values by varying the existing values and determining any change in the rate of climb. A positive change indicates more efficient thrust values, and these will be used to control the engine.
According to a further aspect of the present invention, control apparatus for use with a single lever aircraft engine power control device includes a first input for receiving detected airspeed, a second input for receiving detected air pressure, and a third input for receiving a thrust command from the single lever power control device. A memory stores propeller RPM and MAP commands for predetermined airspeed, air pressure, and thrust command conditions. A processor selects a propeller RPM command and a MAP command from said memory to produce maximum thrust efficiency for the detected air speed, the detected air pressure, and the received thrust command. The processor may also receive the detected actual propeller RPM and the detected actual manifold air pressure and produce a propeller RPM actuator command and a MAP actuator command based on the detected RPM and MAP values and the RPM and MAP commands selected from memory.
According to another aspect of the present invention, apparatus for controlling an aircraft engine having a rotating mechanism and an air inlet includes a single, manually-activated structure for providing an engine thrust command. A processor is provided for receiving the engine thrust command and detected ambient air conditions, and determines first and second control commands for the aircraft engine. The processor determines the first and second control commands based on the received engine thrust command, the detected ambient air conditions, and a maximum thrust efficiency value for the detected ambient air conditions.
According to yet another aspect of the present invention, a method for controlling an aircraft engine with a single lever power control device includes the steps of (i) generating an engine thrust command with a single lever power control device, (ii) detecting ambient flight conditions, (iii) determining an engine rotation command and an engine load command based on the generated thrust command, the detected ambient flight conditions, and a predetermined maximum thrust efficiency value for the detected ambient air flight conditions, and (iv) outputting first and second engine control signals based respectively on the engine rotation command and the engine load command.
According to a further aspect of the present invention, a storage medium for storing computer-readable instructions for causing an aircraft computer to control an aircraft engine comprises instructions for causing the aircraft computer to read a thrust command from a manually-operable, single lever power control device, instructions for causing the aircraft computer to read detected ambient air flight conditions, and instructions for causing the aircraft computer to access a memory with the thrust command and to read therefrom a predetermined engine rotation command and a predetermined engine load command. The engine rotation command and the engine load command are predetermined for maximum thrust efficiency at the detected ambient air flight conditions.